(1) Field of the invention.
The present invention relates to a method and apparatus for catching and removing fine particle dust produced from a source from which fine particle dust is generated, and particularly to a method and apparatus for effectively catching and removing fine particle dust having a diameter of less than about 0.3 .mu.m, which is produced in a process of manufacturing semiconductor elements, and for attempting compactness and miniaturization of the apparatus.
(2) Prior Art
Fine particle dust is generated in a source which belongs to a semiconductor element producing method, automobile manufacturing, plastics manufacture, resources manufacture, ceramics manufacture, powder metallurgy manufacture, cleanser industry, catalyzer manufacture, ferrite manufacture, color material industry, agricultural chemical industry, fertilizer industry, food industry, waste treating industry, bio-chemical industry, cosmetic industry, or medical and pharmaceutical industry.
It is known that very fine particle dust having a diameter of about 0.01-50 .mu.m is produced in such a source of generating the dust.
Recently, computers and electric control devices utilizing the computers have progressed remarkably, and development of these industries have expanded widely and infinitely. Now, a technique in manufacturing semiconductors takes an important position as electronic parts especially those used for a computer, and also the amount of semiconductor production is growing remarkably and rapidly.
Germanium (Ge) and silicon (Si) are normally used as raw materials for semiconductor elements, and as a special semiconductor element, gallium-arsenide (GaAs) and gallium-phosphorus (GAP) and the like are also practiced.
It is well known that fine particle dust generated in the process of manufacturing semiconductor elements is itself harmful in a viewpoint of a public nuisance, which is prohibited to be discharged into the atmosphere, and that the gas including the fine particle dust is itself harmful. Further, it is also well known that the dust adsorbed is a harmful product if released in a gas.
The harmful products generated or used in the semiconductor manufacturing are silicon, arsenic, phosphorus, boron, metallic hydrogen, fluorine, halogen, halide, nitrogen oxides and the like.
Nowadays, one's mind of preventing a public nuisance is thoroughly permeated. In such a state, to directly discharge the exhaust gas including the above harmful components or fine particle dust into the air is not acceptable, and first of all it is required to remove the particle dust from the exhaust gas and give it suitable treatments so as to change the harmful gas to a safe and clean gas.
Then, it is proposed that to remove particle dust from an exhaust gas or the like, the prior art has been using a cyclone, a scrubber, a venturi scrubber, a bag filter, an electric collector, a looper and a settler.
However, the function for catching the particle dust is limited. In the case of the cyclone, the diameter of the particle dust is more than 3.0 .mu.m, and in the scrubber is 1.0 .mu.m. In the case of the venturi scrubber, bag filter, and electric collector, the diameter is more than 0.1 .mu.m. Also, in the looper is 10 .mu.m and the setter is 50 .mu.m. It is a known fact that these conventional devices cannot filter out the fine particle dust having a diameter of 0.01 .mu.m-50 .mu.m.
The venturi scrubber, bag filter, and electric collector may filter out the fine particle dust having a diameter of 0.1 .mu.m, but these apparatus are big and expensive and troublesome in disposal of the waste of the filtered dust.
When actually checking distribution of the diameter of the fine particle dust, which is produced in the process of manufacturing semiconductor elements, it has particles less than about 0.3 .mu.m. Therefore, it has been tried repeatedly to develop an apparatus which may filter dust particles of less than about 0.3 .mu.m from a gas. Through the development, it has been found that dust particles of less than about 0.3 .mu.m may be collected sufficiently by using a filter which comprises a non-woven cloth of felt having a thickness of 1.5 mm.
Then, it was tried to wash the filter with a high pressure fluid against the flow of the gas so as to reuse the filter. However, since the filter has a very small mesh, a relatively high pressure fluid must be used for cleaning the filter. As a result, it necessitates a cleaning apparatus of big and high ability and requires a broad area for its installation. Also, the apparatus becomes very expensive and its maintenance cost increases.
Therefore, as shown in FIG. 5, it is proposed a self-reclaiming dust collector which comprises a filter 101 formed cylindrically to have a vertical axis, a brush 102 disposed rotatably and in contact with the inner periphery of the filter 101, so as to introduce the gas to an end of the brush 102 while rotating the brush 102, and a flow of the gas through the center of the brush 102 via the hollow portion of the filter 101 toward the outside, and then the dust stuck to the filter 101 is brushed off by rotating the brush 102.
However, when the self-reclaiming dust collector is used as the fine particle dust collector in the actual process of manufacturing semiconductor elements, a pressure loss of the filter 101 becomes great within a short period of time which is a shorter time than the anticipated period, and moreover it was found that the filter cannot be reclaimed even if the brush 102 is rotated.
Then, the inventor further researched and found that the acceleration of blockage of the filter was bought on by the following fact. Namely, the gas or air including the fine particle dust produced in the process of manufacturing semiconductor elements, included liquids such as an oil that has leaked from a vacuum pump or an oil or water used for polishing or cutting. The liquids were floating in the state of very small fine mist, and once stuck to the inside wall of a duct while the gas flowed in the duct and separated therefrom due to the flow of the gas and then transferred to the filter 101, so that the liquids adhered to the laminated filter together with the fine particle dust to cause a blockage of the filter 101. Further, the liquids absorbed the fine particle dust floating around the filter 101 and blocked the mesh of the filter 101.
Furthermore, the oil and water that adhered to the surface of the filter 101 permeated into the mesh of the filter 101 according to the pressure of the gas and capillarity and pooled therein. When these adhered to the surface of the filter 101 together with the fine particle dust, it was very difficult to remove those from the filter 101 by scraping the same with the brush 102. As the result, it was confirmed that the filter was blocked and not reclaimed.